"Argument as to what caused it continues, but nobody disagrees that a large carbon isotopic excursion is associated with the initial warming."

Let's take that at its face value, although the text books have already disagreed that it was caused by "a large isotopic excursion", saying that the conventional wisdom was it was caused by Methane calthrates. Maybe if I got my information from Skeptical Science I'd believe that everybody believe that it was caused by CO2, but I don't. The Eocene was certainly a period where CO2 was at 1000ppm(probably caused by the sudden rise in temperature at the end of the PETM) and the temperature was higher than todayss, so what can we expect from our experience of the past, notwithstanding the sea level rises that might occur due to ice melt and thermal expansion:

The Eocene

"Climate

The Eocene global climate was perhaps the most homogeneous of the Cenozoic; the temperature gradient from equator to pole was only half that of today's, and deep ocean currents were exceptionally warm. The polar regions were much warmer than today, perhaps as mild as the modern-day Pacific Northwest; temperate forests extended right to the poles, while rainy tropical climates extended as far north as 45°. The difference was greatest in the temperate latitudes; the climate in the tropics however, was probably similar to today's.

It is hypothesized that the Eocene hothouse world was caused by runaway global warming from released methane clathrates deep in the oceans. The clathrates were buried beneath mud that was disturbed as the oceans warmed. Methane ( CH4 ) has ten to twenty times the greenhouse gas effect of carbon dioxide (CO2 ).

Flora At the beginning of the Eocene, the high temperatures and warm oceans created a moist, balmy environment, with forests spreading throughout the Earth from pole to pole. Apart from the driest deserts, Earth must have been entirely covered in forests. Polar forests were quite extensive. Fossils and even preserved remains of trees such as swamp cypress and dawn redwood from the Eocene have been found on Ellesmere Island in the Arctic. The preserved remains are not fossils, but actual pieces preserved in oxygen-poor water in the swampy forests of the time and then buried before they had the chance to decompose. Even at that time, Ellesmere Island was only a few degrees in latitude further south than it is today. Fossils of subtropical and even tropical trees and plants from the Eocene have also been found in Greenland and Alaska. Tropical rainforests grew as far north as the Pacific Northwest and Europe.

Palm trees were growing as far north as Alaska and northern Europe during the early Eocene, although they became less abundant as the climate cooled. Dawn redwoods were far more extensive as well.

Antarctica, which began the Eocene fringed with a warm temperate to sub-tropical rainforest, became much colder as the period progressed; the heat-loving tropical flora was wiped out, and by the beginning of the Oligocene, the continent hosted deciduous forests and vast stretches of tundra.

Oceans

The Eocene oceans were warm and teeming with fish and other sea life. The first Carcharinid sharks appeared, as did early marine mammals, including Basilosaurus, an early species of whale that is thought to be descended from land animals that existed earlier in the Eocene, the hoofed predators called mesonychids, of which Mesonyx was a member. The first sirenians, relatives of the elephants, also appeared at this time.

It is not my understanding that India had yet reached Asia at the beginning of the Eocene, the consensus in the text books seems to indicate methane released caused by warming oceans:

"At the beginning of the period, Australia and Antarctica remained connected, and warm equatorial currents mixed with colder Antarctic waters, distributing the heat around the planet and keeping global temperatures high. But when Australia split from the southern continent around 45 mya, the warm equatorial currents were deflected away from Antarctica, and an isolated cold water channel developed between the two continents. The Antarctic region cooled down, and the ocean surrounding Antarctica began to freeze, sending cold water and icefloes north, reinforcing the cooling.

The northern supercontinent of Laurasia began to break up, as Europe, Greenland and North America drifted apart.

In western North America, mountain building started in the Eocene, and huge lakes formed in the high flat basins among uplifts, resulting in the deposition of the Green River Formation lagerstätte.

In Europe, the Tethys Sea finally vanished, while the uplift of the Alps isolated its final remnant, the Mediterranean, and created another shallow sea with island archipelagos to the north. Though the North Atlantic was opening, a land connection appears to have remained between North America and Europe since the faunas of the two regions are very similar.

India continued its journey away from Africa and began its collision with Asia, folding the Himalayas into existence."

"Slow change in forcing = slow change in T. Fast change in forcing = fast change in T. The physics remains unchanged on all time scales"

This is simplistic and wrong.

A force 'X', with the potential of making a rapid measurable change in the system can be trapped in a conundrum, faced off against a myriad of opposing and distracting forces. The resulting global change would then occur over a much longer period than it is otherwise capable of producing. If the opposing forces are ill-understood or their existence undiagnosed, one may wrongly conclude that X can only produce 'slow' change, or worse, that 'X' is therefore a weak force. Or, if the opposing forces change phase and act in concert with 'X' than against it, one may conclude that the 'system is very sensitive to change in X' just as one would conclude the opposite in the former situation. All above conclusions would be wrong.

In fact, that scientists trot out something similar to the above as explanation to climate phenomena even at much shorter time periods, while propagating a simple 'CO2 is the only forcing known to man and God' idea at the same time, is quite evident: 'Why did the 21st century not warm as you said it would? Because chinese factory smoke and ocean water swallowed the heat. Does that mean they are as powerful as CO2? Let us not go there.'

Would you consider the collision of India with the Eurasian landmass a slow forcing or a rapid forcing?

I feel, since I started this discussion, that I ought to make some contribution but frankly I am losing the will to live.I think I am finally coming round to the view that, as Rhoda said, "global" warming doesn't exist (have I got that right) and that everything from forcings to feedbacks works at the local/regional level and attempts to extrapolate are doomed to failure.Neither do I hear or read anything that convinces me that increased water vapour will not in the long run result in increased clouds and I can see no reason to part from the theory that increased cloud cover will have a net cooling effect.I have still not heard any reason why the forcings and their feedbacks that drive the earth into and out of ice ages must be the same as those that drive the assorted warm and cold periods that we have been discussing.Given that the only answer I got to the question of what forcing initiated the Roman and Mediaeval Warm Periods was "dunno" I fall back on what I said earlier that if you don't know what started the last two warm periods then you don't know what started this one.I am inclining more and more to the views of Nikolov & Keller. Since CO2 is evidently not the driver for the recently observed warming on other planets (Mars, for example) perhaps their hypotheses are worth a closer look.

PS One reason for the sparseness of posting yesterday and today was that I was waiting for news of the birth of my grandchild who now turns out to be a grand-daughter. Normal service will be resumed in the next couple of days.

All we need for a proof of Nikolov and Keller is a planet with an atmosphere and no sun. Personally I think the temp would be the same at all altitudes, but I am not sure. I AM sure that this would not break conservation of energy as their supporters claim.

The 100,000-year timescale in the glacial/interglacial cycles of the late Pleistocene epoch (the past ~700,000 years) is commonly attributed to control by variations in the Earth's orbit1. This hypothesis has inspired models that depend on the Earth's obliquity (~ 40,000 yr; ~40 kyr), orbital eccentricity (~ 100 kyr) and precessional (~ 20 kyr) fluctuations2, 3, 4, 5, with the emphasis usually on eccentricity and precessional forcing. According to a contrasting hypothesis, the glacial cycles arise primarily because of random internal climate variability6, 7, 8. Taking these two perspectives together, there are currently more than thirty different models of the seven late-Pleistocene glacial cycles9. Here we present a statistical test of the orbital forcing hypothesis, focusing on the rapid deglaciation events known as terminations10, 11. According to our analysis, the null hypothesis that glacial terminations are independent of obliquity can be rejected at the 5% significance level, whereas the corresponding null hypotheses for eccentricity and precession cannot be rejected. The simplest inference consistent with the test results is that the ice sheets terminated every second or third obliquity cycle at times of high obliquity, similar to the original proposal by Milankovitch. We also present simple stochastic and deterministic models that describe the timing of the late-Pleistocene glacial terminations purely in terms of obliquity forcing.

Emphasis added.

Milankovitch theory (not hypothesis, note) is routinely misunderstood. The problem is that people (including myself) tend to talk about the '100ka cycle' when there is in fact no such thing. The variables are eccentricity (~100ka period), obliquity (~41ka period) and precession (~26ka period). The 100ka eccentricity period *is itself* variable over a ~400ka period. The head-exploding combination of these four variables is that eccentricity modulates and amplifies the effects of obliquity and precession and does so differently over time. The complex and shifting interplay results in the 82 - 123ka range of spacing between late Pleistocene interglacial peaks.

Let's take that at its face value, although the text books have already disagreed that it was caused by "a large isotopic excursion", saying that the conventional wisdom was it was caused by Methane calthrates.

Oh dear. Look, the large carbon isotopic excursion is the *fingerprint* of what was quite possibly a huge release of methane from clathrates. You are horribly confused, aren't you?

First, congratulations on the birth of your granddaughter. It's always nice to have a sprinkling of good news to lighten up these discussions :-)

Second, who says it's warming on Mars? There's a common misconception based on albedo change, but it's one of those sceptic memes that turns out to be nonsense. I think there was a paper that compared planetary albedo in 1979 (?) with another snapshot several decades later and jumped to the wrong conclusion. The first (higher) albedo was the result of a planetary-scale dust storm.

I think I am finally coming round to the view that, as Rhoda said, "global" warming doesn't exist (have I got that right) and that everything from forcings to feedbacks works at the local/regional level and attempts to extrapolate are doomed to failure.

Of course global warming exists. You can see for yourself using a rather nifty data visualisation tool provided by NASA. Go here, scroll down to 'Global surface temperature' and have a play with the 'Time series 1884 - 2010' visualisation. Slowly drag the slider below the window to the right. What you see - that's global warming.

BBD, you are posting hypotheses as if they were confirmed fact. Nobody can know for sure what happened so far in the past. They can present ideas, and they do, but all we can do is see whether they fit what we do know. and that isn't much. You can't explain climate over geologocal timescales. You can only have a guess.

And your suggestion that conservation of energy is violated does not work in an open system. 1% extra albedo will blow away all the heat from man-made CO2. There can be no appeal to conservation of energy in climate.

And your suggestion that conservation of energy is violated does not work in an open system. 1% extra albedo will blow away all the heat from man-made CO2. There can be no appeal to conservation of energy in climate.

All we need for a proof of Nikolov and Keller is a planet with an atmosphere and no sun. Personally I think the temp would be the same at all altitudes, but I am not sure. I AM sure that this would not break conservation of energy as their supporters claim.

Aug 3, 2012 at 5:34 PM | rhoda>>>

You have obviously not read their theory.

Insolation is an essential contributor to lower tropospheric temperature. Read it and you'll understand why.

The highest temperature must be at the lowest altitudes where atmospheric pressure, ergo kinetic energy, is at the maximum, as per the ideal gas laws.

Their theory is based on well researched empirical data for nearly all atmospheric Solar System bodies, as opposed to atmospheric CO2 metaphysics.

Readers may be interested in Roy Spencer's disassembly of Nikolov & Zeller.

Aug 3, 2012 at 8:31 PM | BBD>>>>

Somebody else who comments on what he has not bothered to study.

Spencer still makes the same mistake as the IPCC in estimating the Earth's ATE at 33K, without even bothering to compare this to the figure N&K derive from the empirical NASA Lunar Diviner data showing an ACTUAL grey body ATE of 133K. Meaning Spencer has misquoted the warming effect of the atmosphere by an error of 100K - an impossible amount for CO2, or any other so called greenhouse gas, to make up.

His so called "disassembly" is simply a shambolic repeat of flawed IPCC data.

bbd, it's an open system, this climate thing. Energy is conserved in the universe but it does not have to stay in the earth/sun system. Therefore it is not possible to appeal to conservation of energy within that system. Energy is entering and leaving all the time. Maybe, just maybe, you can assume an approach to radiative balance, but even equilibrium is never attained. Because it is all local.

RKS, I certainly never bought the 33C as an argument. When I tried to get a grip of N&K I could not get what they were talking about. I stayed away from the copious nonsense which accompanied that debate and ended up no wiser. Basically I don't know how to transfer conditions on other planets to here. Too many things different, of which a short day and the presence of lots and lots of water in all forms are (to me) the major factors. I do not believe that CO2 is the only thing keeping us from freezing.

RKS, I certainly never bought the 33C as an argument. When I tried to get a grip of N&K I could not get what they were talking about. I stayed away from the copious nonsense which accompanied that debate and ended up no wiser. Basically I don't know how to transfer conditions on other planets to here. Too many things different, of which a short day and the presence of lots and lots of water in all forms are (to me) the major factors. I do not believe that CO2 is the only thing keeping us from freezing.

I don't argue against 'alternative' versions of atmospheric physics. If N&Z are on to something, then it's just a matter of time before the whole CAGW house of cards comes tumbling down. All we have to do is wait.

And a little change in albedo alters the incoming. Which itself varies in all wavelengths over time and because of the elliptical orbit. That in itself is 10% over the year. Energy arrives and energy leaves. It's an open system. We have (at least) two systems for measuring albedo. They don't agree. And yet in BBD world all is certainty. IMHO certainty is more likely an indicator of wrongness than doubt is.

Now read the theory THOROUGHLY before commenting on it please.I don't argue against 'alternative' versions of atmospheric physics. If N&Z are on to something, then it's just a matter of time before the whole CAGW house of cards comes tumbling down. All we have to do is wait.

In the mean time, I'll stick with the standard position.

Aug 3, 2012 at 9:33 PM | BBD>>>>

Have you read Judith Curry's essay regarding the dangers of IPCC 'Concensus' science - or don't you have enough knowledge and imagination to actually THINK about what science, and the scientific method, is really all about?

BLIND FAITH in what others say regarding the natural world is religion - repeating it from a faith based viewpoint is dogma.

Now read the theory THOROUGHLY before commenting on it please.I don't argue against 'alternative' versions of atmospheric physics. If N&Z are on to something, then it's just a matter of time before the whole CAGW house of cards comes tumbling down. All we have to do is wait.

In the mean time, I'll stick with the standard position.

Aug 3, 2012 at 9:33 PM | BBD>>>>

Isn't 15 years of global temperatures remaining stable [Met Office blog for one source], while CO2 levels continue rising, enough to make you wonder just a little bit about the "standard position"?

Especially as BEST has now been rubbished and law suits in Canada and NZ are pursuing upwardly doctored temperature data.